thyroid hoemones effect gastric acid and pepsin secretion.however exact machanism(s) are not clear.this study was performed to compare the effect of vagal stimulation on acid an pepsin secretion in hypothyroid,hyperthyroid and control rars.each group consisted of 8 male and female rats(N-mari) weighing 246+_9 gr.hypo and hyperthyroid states were induced by administretion of methimazol (50mg/l in drinking water)and thyroxine (500mg/l in water) for 20 and 35 days respectively.animals housed in standard conditions (12hr:12hr light/dark) and were deprived of food for 24 hours befour study.under general anesthesia,animale underwent tracheostomy,laparatomy and vagotomy.a cannula was inserted into stomach via duodenum for collection of gastric juice.after 30 minutes of recovery,peripheral and of vagus nerve was stimulated for 15 minutes,and acid and pepsin outputs were measured in collected gastrik samples.acid out put during 15 minutes vagus nerve stimulation were 19.6+_1.4,56.7+_0.8 and 45.1+_0.9 mol,in hypothyroid,hyperthyroid and control groups respectively.similarly ,pepsin secretion during this period was 1.3+_0.09 and 12.4+_0.3 mg.in hypo and hyperthyroid groups respectively.which shows significant differnces with the control group(5.9+_0.4mg).from the results of this study it appears that,thyroid hormones can alter gastric acid and pepsin secretion in response to vagal stimulation.